The woman known as Cecilia Reyes was originally born into a poor family in a poverty-stricken neighborhood, living with her parents and her brother. Not much is known about Cecilia’s childhood, save for one tragic incident when she was six years old. The young girl bore witness to the death of her father, who was gunned down for reasons unknown. Powerless, Cecilia could do nothing for her father except to hold him in her arms as he bled to death on the sidewalk. It was when her father died that the helpless Cecilia made a vow that one day she could do something. Reading her brother’s science textbooks that night, she knew that she wanted to become a doctor, so that she could help other people. Thanks to her stubbornness, Cecilia spent nineteen years studying and made her way out of her poor neighborhood and went to medical school, eventually becoming an intern doing her residency at Our Mother of Mercy Hospital in the Bronx - all the while keeping her mutant powers a secret. [X-Men (2nd series) #66]

Somewhere along her journey, Cecilia was approached by a teacher, Professor Charles Xavier, who had recognized her as a mutant. He offered her to come to his school to receive proper training in the use of her mutant powers, and eventually to join his X-Men. However, Cecilia was not ready to accept the fact that she was a mutant and did not want any dealings with super-heroics in general. Her focus was to save lives as a doctor. Respecting her decision, Xavier bid Cecilia goodbye, promising to keep her identity secret. Cecilia went on with her studies, all the while fearing what would happen one day if the people around her found out that she was a mutant. [Uncanny X-Men (1st series) #389] The next three years passed without incident.

When Operation: Zero Tolerance, a government sponsored program that used humans as Prime Sentinels to locate and capture mutants, kicked into high gear, the Xavier Institute was compromised and most available X-Men were captured. Cecilia watched news coverage of Operation: Zero Tolerance from the hospital, while her fellow co-workers and patients cheered. Fearing discovery, Cecilia pretended to be a mutant-hater as well. However, the next day, their celebrations were interrupted by the arrival of a gunshot victim. Unfortunately, Cecilia was unable to save the man’s life and she declared him dead. The man, however, was not dead, as he transformed into a Prime Sentinel and began to assault Cecilia, revealing her mutant status to all her co-workers and friends. Fortunately, Cecilia’s powers saved her from the assault, her psioplasmic bio-field protecting her from every attack, though she still would feel every gut-wrenching blast.

Eventually the Sentinel would have found a way to negate her force-field, but Cecilia was saved by the timely arrival of Iceman. However, Cecilia was not pleased to see Iceman and hit him, angry that Xavier did not keep his promise and that the X-Men had dragged her into what she perceived to be their self-fulfilling war games. While he took Cecilia to the Morlock Tunnels to hide from their pursuers, Iceman explained to her that this incident was beyond Xavier and the X-Men, and convinced her that the only way to survive was to follow him, and perhaps the X-Men could make a new tomorrow for her. Knowing that her lifelong goal of being a doctor was gone, Cecilia reluctantly agreed to accompany Iceman - on her own conditions. She demanded the absolute truth from Iceman, even making him reveal his secret identity of Bobby Drake to her.

The pair soon reached Soho and Cecilia quickly proved to be a feisty one, with sarcastic comments and rude one-liners. At the empty city apartment of Warren Worthington, aka Iceman’s teammate Archangel, the two were attacked by yet another Prime Sentinel, only this time to be saved by Detective Charlotte Jones. She took Cecilia and Bobby to her precinct, actually leading them into a trap set up by Bastion, the leader of OZT, who was holding Charlotte’s son hostage. Later, Charlotte saw the error in her deal and defended Cecilia and Iceman, resulting in her getting shot. Not only did Cecilia tend to Charlotte’s wound, but during the battle with the Sentinels she also covered Iceman’s back by taking any attack aimed at him with her shield, despite the pain this caused her or the grievances she had with the X-Men. [X-Men (2nd series) #65-67]

Eventually, the pair were joined by mutant terrorist Marrow and Israeli super-soldier Sabra, with both of whom Cecilia entered verbal fights. With Sabra’s information, the group located Bastion in his Connecticut home and confronted him, only to end up completely outnumbered by an entire army of Prime Sentinels. In the meantime, though, the US government revoked Bastion’s rights to operate his organization on American soil and a timely arrival by S.H.I.E.L.D. at Connecticut ended the battle before it even started. [X-Men (2nd series) #68-69]

Both Cecilia and Marrow accepted Iceman’s invitation to accompany him to the Xavier Institute but, when they arrived there, Cecilia was crushed to discover that the mansion was completely empty. Bastion’s forces had even scraped the paint off the walls. The stress came closing down on Cecilia, who realized that she followed Iceman for nothing - her life was in ruins, and the X-Men had no hope to offer. It was right then that the group of X-Men captured by Bastion returned home as well, among them Cyclops, who was dying of a bomb placed in his abdomen by Bastion. Overhearing Cyclops and Phoenix talking and expressing their love, Cecilia put her fears behind her and focused on helping Cyclops. She immediately took charge and put all the X-Men to work on securing medical equipment and prepping Cyclops for surgery. Under the leadership of Cecilia, the X-Men were able to save Scott, despite an unfortunate intrusion by Juggernaut. After his surgery, Cyclops was the first to welcome Cecilia to the team, though she ignored his offer to join. [X-Men (2nd series) #70]

Cecilia spent the next few days at the mansion, unsure what to do next. During this time, she put up a tough and sarcastic attitude towards everyone, though actually Cecilia began to make some friends among the X-Men. A slip of the tongue even led to mild flirtations with the Beast, much to Cecilia’s embarrassment, though he took it with humor. Both of them being interested in medicine and physiology, they were eager to study how Marrow’s bone-growth worked and discussed other scientific topics as well. Cecilia even placed a friendly wager as to when Beast would cure the Legacy Virus. [X-Men (2nd series) #71, 73]

Eventually Cecilia tried to reclaim her internship at Our Mother of Mercy. At first, her superior, Dr. Gibbons, was hesitant to give Cecilia her position back, as he knew not everyone at the hospital would be willing to accept her, but Cecilia was able to convince him to give her a second chance. However, before her first surgery, Cecilia was pulled out by Gibbons, as the family of the victim didn’t want a mutant working on their son.

Apparently someone on Cecilia’s surgical team had revealed her status to the family. After enduring several similar incidents with intolerant co-workers, Cecilia was found by the injured Daredevil, who was watching Cecilia and felt he could trust her to help with his gunshot wound. While treating Daredevil, the hero told Cecilia that she should use her gift. He reasoned that, as a doctor, she could only save one person at a time, whereas as a mutant she could save thousands in an instant. Later that day, the injured villain Pyro was brought in and Cecilia was put in charge of the case. However, during recovery, Pyro tricked Cecilia into loosening his straps that the police put on him. He then escaped, resulting in Cecilia losing her job. Fired after only one day, Cecilia returned to the X-Men for good it seemed. [Uncanny X-Men (1st series) #351]

Sometime later, Marrow stole Cecilia’s medical bag in order to help the injured Callisto, her former mentor. When Cecilia gave chase in her anger, she involuntarily used her force field offensively for the first time, in this case to get Beast out of her way. [X-Men (2nd series) #73]

Cecilia’s fears of helplessness and inadequacy caught up to her later when the demons known as the Ru’tai materialized on the grounds of the Xavier estate. Face to face with demons, something she had not believed possible, Cecilia panicked and found herself running for her life.

When things settled for a moment, she confronted Beast with her fear of being worthless. However, Cecilia was captured alongside most of the X-Men by the Ru’tai and taken to their home dimension. Once there, the Ru’tai tried dissecting Cecilia, but again her force field protected her. When the X-Men fought back, Cecilia at first hid by the sidelines, observing the battle and asking herself how the X-Men could defeat these foes. It was Maggott who reminded her that she was now part of the X-Men and inspired her to feel that way. Wanting to make her dead father be proud of her, Cecilia beat back her fears and charged into battle. Actually, she saved the day when she fell on the talisman that powered the Ru’tai reality, breaking it with her butt. Nonetheless, that day Cecilia’s doubts slowly began to fade away and she felt more like she belonged. [X-Men (2nd series) #75]

When the X-Men were attacked by the Shadow King, he tried to corrupt the newer X-Men, tempting them with their secret desires. He offered Cecilia a new future with her own operating room and the knowledge the world’s best surgeons. Still, she was concerned about her fellow X-Men's fate and had not yet reached a decision when the Shadow King was eventually defeated by Storm and Psylocke. Afterwards, Cecilia took charge of helping the injured people of Storm’s village, thus redeeming herself for letting herself be tempted. [X-Men (2nd series) #77-78]